The present invention relates to an implant assembly. In particular, but not exclusively, the present invention relates to an implant assembly for implanting a resurfacing implant to replace an articulating surface at the end of a bone which forms the ball component of a ball and socket joint. Certain embodiments of the present invention comprise an implant that is provided with a roughened bone engaging surface to prepare the bone surface so as to accurately shape the end of the bone to fit a cavity within the implant. Embodiments of the implant assembly further includes a spacer sleeve releasably coupled to the implant during the bone preparation in order to position the implant correctly relative to the bone.